1. Field of the Invention
The present invention relates to a method for manufacturing an active layer of a solar cell, and, more particularly, to a method for manufacturing an active layer including multiple micro cavities in sub-micrometer scale which can increase the photoelectric conversion rate of a solar cell.
2. Description of Related Art
The conventional energy for human society such as uranium, natural gas, and petroleum will be used up in future decades. The scientists therefore pay lots efforts to develop alternative energy such as solar energy, wind energy, wave energy, and earth heat.
However, the application of wind energy, wave energy, or the earth heat is limited by the geometrical regions such as the neighborhood of volcano, or that of sea shore. Moreover, most equipment required for the application of wind energy, wave energy, and earth heat is huge. Hence, the solar energy with high convenience attracts scientists' attention.
So far, many materials are used in the solar cells. Without surprise, the photoelectric conversion rates of various materials differ a lot. Generally speaking, current solar cells can be categorized into three major styles, i.e. silicon series solar cells, III-V series solar cells, and II-VI series. The silicon series solar cells include solar cells made of single crystal silicon, poly silicon, and amorphous silicon matrix. The III-V series solar cells include solar cells made of gallium arsenide matrix, indium phosphide matrix, and gallium indium phosphide matrix. The II-VI solar cells include the solar cells made of cadmium selenide matrix, and or copper indium selenide matrix. The maximum photo electro conversion rates of the solar cells are: single crystal silicon 24.7%, poly silicon 19.8%, amorphous silicon 14.5%, gallium arsenide 25.7%, and copper indium selenide 18.8%, individually. In fact, the photoelectric conversion rate for the solar cells in laboratory can be about 30%. However, the photoelectric conversion rate for the commercial solar cells is lower than 20%. Hence, the photoelectric conversion rate for the commercial solar cells still needs to be improved. Currently, the commercial solar cells are mainly made of single crystal silicon or poly silicon since the cost for mass production is relative low and the photoelectric conversion rate is acceptable.
However, the price of the solar cells is still high since more than half of the cost of the solar cells is the cost of the silicon matrix. Hence, scientists try to find the new materials for solar cells and improve the manufacturing process to reduce the cost. So far, the most effective option for reducing the cost and increasing the photoelectric conversion rate is to increase the photo-absorption area of the solar cells (e.g. using nanorod as materials for photoreaction) or to increase the number of the projected photons (e.g. applying an antireflection layer). But the manufacturing process for the solar cells containing nanorod is very complicated. Many metal catalysts are required to facilitate the formation of nanorods. Therefore, the cost increases since many metal catalysts are required. Furthermore, the metal catalysts also act as impurities in the solar cells to interfere the migration of electrons in the solar cells. Of course, the photoelectric conversion rate decreases. On the other hand, the formation of anti-reflection layer needs complicated photomasks to shape the surface into a pyramid-form. Then deposition is introduced to form anti-reflection layer. All this complicate process increase the cost of solar cells a lot, lower down the yield, and is not suitable for mass production.
Therefore, it is desirable to provide a solar cell with improved photoelectric conversion rate and method for manufacturing the same to mitigate the aforementioned problems.